1. Field of the Invention
The present invention generally relates to ink-jet printing and specifically relates to deciding a position of a trailing end in a direction of conveyance of a recording sheet.
2. Description of the Related Art
In recent years, the technology for printers has made rapid progress according to the development of personal computers. The printers record images on sheets based on image information. Recording means for the printers that attracts attention most in recent years is an ink-jet recording system. An ink-jet recording system that record an image by ejecting an ink on a sheet from a recording head have become common. The advantages of the ink-jet recording system are that the ink-jet recording system can record a high-definition image at high speed and is more excellent than other recording methods in various points such as running cost and quietness.
Some ink-jet printers cause a charged belt, to attract a recording sheet and secure flatness of the recording sheet to write an image on the recording sheet. In this type of ink-jet printer, it is necessary to prevent an ink from adhering to the belt because of an error in size of the recording sheet. To solve this issue, this type of ink-jet printer includes a mechanism for detecting a position of a trailing end or an amount of margin of the recording sheet to prevent misrecording on the belt.
Specifically, in this type of ink-jet printer, a registration roller is provided on an upstream side in a conveying direction with respect to a carriage mounted with a print head and movable in a main scanning direction and a registration sensor is provided further on the upstream side than the registration roller. A position of a trailing end of a recording sheet is detected based on a detection signal of the registration sensor and an amount of conveyance of the recording sheet in a conveyance mechanism is calculated from a remaining printable distance or the like.
However, in a control system in the mechanism mounted on the printer of the ink-jet recording system, detection by a trailing-end detection sensor is monitored in polling by software and processing for absorbing chattering is required. Thus, a time lag occurs between an instance when this sensor is actually turned off and time when the software recognizes a result of the turn-off of the sensor. Therefore, it is likely that the recording sheet is conveyed until the turn-off of the sensor is decided and the position of the trailing end of the recording sheet deviates from a position where of the trailing-end detection sensor is turned off.
For example, Japanese Patent No. 3687634 discloses a printer that calculates a distance of sheet conveyance at low speed and a distance of sheet conveyance at high speed using two sensors and two measuring units, calculates a response delay time of the upstream side sensor from these two sheet conveying direction, and corrects a remaining printable distance on a sheet trailing end side using this response delay time.
Japanese Patent Application Laid-Open No. 2003-94746 discloses a recording apparatus that corrects, according to a characteristic of a detection delay of a detecting unit, a position of a recording medium corresponding to a recording position of a recording head stored by a conveyance history storing unit, evaluates an amount of margin of the recording medium based on positions of the recording medium before and after the correction, and controls a recording operation based on a result of the evaluation.
In the invention disclosed in Japanese Patent No. 3687634, the two sensors that detect a position of a trailing end of a recording sheet are used and a response delay time (a time lag) is calculated and corrected using measured values of conveyance speed and a conveyance distance. Thus, when performance of the sensors falls and an error occurs in a detection result, it is impossible to obtain an accurate position of the trailing end. Therefore, it may be necessary to use a correction value set in advance.
In the invention disclosed in Japanese Patent Application Laid-Open No. 2003-94746, a true detection time is calculated from a detection delay characteristic (a detection delay time) set in advance and a conveyance history (a sensor detection time). Correction for calculating a true detection position based on this true detection time is performed. It is preferable for more accurately obtaining a position of a trailing end of a recording sheet to use not only the calculation of a position of the trailing end of the recording sheet by a sensor but also other methods.
Thus, there is a need of a technology that can accurately detect a position of a trailing end and a recordable area of a recording sheet by using inexpensive configuration.